Variable optical element, a pickup apparatus having the variable optical element, and an information recording and reproducing apparatus having the pickup apparatus

ABSTRACT

An information recording/reproducing apparatus of the invention is equipped with an objective lens, a light source and a variable optical element having a grating which demonstrates a piezo-electric effect by means of an electric field. The light source emits and irradiates a laser beam onto the grating to generate a 0th order diffraction beam and +/− 1st order diffraction beams in accordance with first order diffraction efficiency, and the objective lens converges the 0th diffraction beam and +/− 1st order diffraction beams which are irradiated onto an information recording medium for the purpose of information recording or information reproducing. By controlling an electric field applied to the grating, the first order diffraction efficiency of the grating is adjusted, whereby light beams are generated which have power levels appropriate for various kinds of information recording media.

This application is a divisional patent application under 37 C.F.R. §1.53(b), of prior application Ser. No. 09/739,646 filed on Dec. 20, 2000now U.S. Pat. No. 6,628,599.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable optical element that iscapable of, for example, altering optical characteristics such asdiffraction efficiency, a pickup apparatus that comprises the variableoptical element, and an information recording and reproducing apparatusthat comprises the pickup apparatus to carry out the recording ofinformation to and reproduction from information recording media.

2. Description of the Related Art

In recent years, information recording media having recordableproperties other than information recording media havingreproduction-only properties and of a phase-change type have receivedattention as high-density and large-capacity information recordingmedia. Among the phase-change type information recording media,write-once optical discs that allow one-time recording of informationand rewritable optical discs that allow erasing and rewriting ofinformation have been received attention.

These phase-change type information recording media have a layeredstructure, as shown in the sectional view of, for example, comprising alight-incident layer onto which a light beam is made incident from anobjective lens provided in a so-called pickup apparatus, a recordinglayer of a crystal or amorphous material protected by a protectionlayer, a reflective layer, and a substrate, and are so configured thatinformation is recorded by effecting phase changes to the recordinglayer by the light energy of a light beam. Reproduction of informationis carried out by first irradiating a light beam onto the recordinglayer, which reflects the beam, then converging rays of reflected lightwith the objective lens, and finally detecting the reflected light witha photodetector of the pickup apparatus.

Write-once optical discs have a characteristic whereby they are capableof recording information only once, which is provided for by having arecording layer whose phase is changed (an irreversible change)according to light energy. Erasable optical discs have a characteristicwhereby they are capable of rewriting information, which is provided forby having a recording layer whose phase is changed (a reversible change)according to light energy. In addition, the recording density of theseinformation recording media are increased by narrowing the track pitchof the recording layer and further increases in recording capacity arerendered by adding more recording layers.

It is considered, on the other hand, that a light beam of a smallerfocused spot diameter is irradiated onto a recording layer by using agreater numerical aperture (NA) of an objective lens provided in apickup apparatus in order to realize an information recording/rewritingapparatus that keeps pace with the above mentioned high-densityinformation recording media.

However, while increasing the numerical aperture (NA) of the objectivelens corresponding to narrower track pitches of information recordingmedia, it is important to carry out high-density information recordingand appropriate information reproduction within the limited range of thenumerical aperture (NA) of the objective lens. As a response to thisproblem, attention has been given to the usefulness of applying acrosstalk cancellation technique when reproducing information.

A crosstalk cancellation technique is such that not only a light beam is(referred to as the main beam) irradiated onto a track in whichinformation is recorded (referred to as the main track) to read theinformation from it but also light beams (referred to as the sub-beams)are irradiated onto the tracks next to the main track (referred to asthe adjacent tracks) to read information from them as well, whereupon byexecuting a predetermined calculation based upon the main signalobtained from the main beam and the sub-signals obtained from thesub-beams, a crosstalk component contained in the main signal iscontrolled to reproduce information with a good accuracy.

In addition, a method is considered to diffract a laser beam emittedfrom a laser light source with the use of a diffraction grating in orderto generate the above mentioned main beam and sub-beams, and therebyirradiate the 0th order light as the main beam and +/− 1st order lightas the sub-beams onto each corresponding track through an objectivelens.

However, while above mentioned crosstalk canceling technique is appliedto the reproduction of information from a reproduction-only informationrecording medium such as a DVD-ROM (digital versatile disc read onlymemory), which proves effective in reproducing information with goodaccuracy, if it is applied to the reproduction of information recordedon a phase-change type information recording medium such as aDVD-RW(digital versatile disc rewritable), it poses problems asdescribed below.

In the case of a phase-change type information recording medium, thephase of the recording layer alters corresponding to the amount of lightenergy exerted. For this reason a problem is caused where, whenreproducing information from a phase-change type information recordingmedium, irradiating the above mentioned main beam and sub-beams used fora reproduction-only information recording medium against thecorresponding main track and sub-tracks of the phase-change typeinformation recording medium imparts phase changes to the recordinglayer of the main track and/or sub-tracks to erase or destroyinformation that was recorded. In other words, a problem occurs where,if the same light beam is applied to both a reproduction-onlyinformation recording medium and a phase-change type informationrecording medium, it is suitable for one type of information recordingmedium but not suitable for the other type of information recordingmedium.

To avoid such a problem, a method can be considered to adjust the lightenergy levels of the main beam and sub-beams, by replacing thediffraction grating with another having a different diffractionefficiency for each particular case, depending on whether information isrecorded to a phase-change type information recording medium, orinformation is reproduced from a phase-change type information recordingmedium, or where information is reproduced from a reproduction-onlyinformation recording medium which is not of a phase-change type.However, this method will give way to a problem in which a ratherlarge-scale mechanism is required to replace one diffraction gratingwith another.

In addition, replacing the grating causes another problem where opticalcharacteristics of the optical system including the above mentionedobjective lens may become unstable.

Further, since replacement of the diffraction grating will take sometime, when, for instance, recording and reproducing information to andfrom a phase-change type information recording medium is repeated oneafter the other, it will give rise to the problem of responsiveness inthat recording and reproduction of information may not be carried outrapidly.

OBJECTIVES AND SUMMARY OF THE INVENTION

The present invention is made to overcome such conventional problems andholds an objective to provide a variable optical element that allowsappropriate recording and reproducing of information to and from aninformation recording medium, an apparatus having such a variableoptical element, and an information recording/reproducing apparatushaving such a pickup apparatus.

Additionally, if a crosstalk cancellation technique is applied, it isanother objective of the present invention to provide, a variableoptical element that provides for performing information recording andreproducing with compatible with both a phase-change type informationrecording medium and a reproduction-only information recording medium, apickup apparatus, and an information recording/reproducing apparatus.

In a first aspect of the invention, a variable optical element takes thestructure wherein the first area having a piezo-electric medium layerwith a piezo-electric effect and the second area that does not have thepiezo-electric layer are formed on the top surface of a reference mediumand imparts optical changes to the wave front of the light incident onthe first and the second areas and reflects it based upon changes in theoptical characteristics of the first and the second areas which arecaused by the piezo-electric effect of the piezo-electric medium layer.

In a second aspect of the invention, a variable optical elementcomprises a piezo-electric medium layer with a piezo-electric effect,which has at least a first area and a second area with differentthicknesses, and which imparts optical changes to the wave front of thelight incident on at least the first and the second areas and reflectsit based upon changes in optical characteristics which are caused by thepiezo-electric effect of the piezo-electric medium layer of at least thefirst and the second areas.

According to the first or the second aspect of the invention, when apiezo-electric medium layer is distorted by the piezo-electric effect,optical characteristics of the first and the second areas are changed, avariable optical element causes optical changes to the wave front of thelight incident on the first and the second areas and reflects it. Thus,by controlling the piezo-electric effect of a piezo-electric layer,various changes can be imparted to the incident light, which, forexample, allows such effects as the appropriate control of the opticalcharacteristics of a light beam irradiated onto an information recordingmedium for the purpose of recording or reproducing information.

In a third aspect of the invention, the variable optical elementaccording to the first or the second aspect further has a plurality ofpairs of the first and the second areas formed in a cyclic manner.

The variable optical element with such a structure also causes opticalchanges to the wave front of the light incident on the first and thesecond areas and reflects it when a piezo-electric medium layer isdistorted by the piezo-electric effect, the optical characteristics ofthe first and the second areas are changed. Based on this behavior, bycontrolling the piezo-electric effect of a piezo-electric layer, variouschanges can be imparted to the incident light, which, for example,allows such uses as to appropriately control the optical characteristicsof light beam irradiated onto an information recording medium for thepurpose of recording or reproducing information.

In a fourth aspect of the invention, the piezo-electric medium layer ofthe variable optical element according to the first or the third aspectabove changes in thickness as a result of the piezo-electric effectcorresponding to voltages externally applied and alters the diffractionefficiency for the light incident on the first and the second areasbased upon phase changes in the first and second areas which areimparted by the changes in thickness.

The variable optical element with such a structure also causes opticalchanges to the wave front of the light incident on the first and thesecond areas and reflects it when a piezo-electric medium layer isdistorted by the piezo-electric effect, the optical characteristics ofthe first and the second areas are changed. Based on this behavior, bycontrolling the piezo-electric effect of a piezo-electric layer withelectricity, various changes can be made to the incident light, which,for example, allows such uses as to the appropriate control of theoptical characteristics of a light beam irradiated onto an informationrecording medium for the purpose of recording or reproducinginformation.

In a fifth aspect of the invention, a pickup apparatus which comprisesthe variable optical element according to the fourth aspect, irradiatesa light beam for recording information onto an information recordingmedium or a light beam for reproducing information from an informationrecording medium onto the information recording medium, wherein a lightsource that emits light toward the first and the second areas of thevariable optical element, and an optical system to generate thelight-beam for recording information or the light beam for reproducinginformation based upon diffracted and non-diffracted light rays that arecaused when the variable optical element diffracted the light emittedagainst it are applied.

In the pickup apparatus of the invention having such a structure, basedupon diffracted and non-diffracted light rays that are effected when avariable optical element diffracts the light emitted from a lightsource, an optical system generates a light beam for recordinginformation or a light beam for reproducing information to irradiate itonto an information recording medium. Based on this, by controlling anelectric field or a voltage to be applied on a variable optical element,for example, it is possible to generate a light beam having powersuitable for recording information on an information recording medium ora light beam having power suitable for reproducing information from aninformation recording medium. In a sixth aspect of the invention, thepickup apparatus according to the fifth aspect further has aphotodetector to detect reflected light which is effected when theinformation recording medium reflects the light beam.

In the pickup apparatus with such a structure, the photodetector detectsreflected light, which is originally a light beam for recordinginformation irradiated to an information recording medium and therebyreflected by it, and the photodetector provides for the generation ofcontrol signals for processing an appropriate recording of informationbased on the results of detection. In addition, this photodetectordetects reflected light, which is originally a light beam forreproducing information irradiated to an information recording mediumand thereby reflected by it, and the photodetector provides for thegeneration of control signals for processing appropriate informationreproduction based on the results of detection.

In a seventh aspect of the invention, an informationrecording/reproducing apparatus contains the pickup apparatus accordingto the sixth aspect above and, has a means to control at least thevoltages applied to the piezo-electric medium layer between the power ofthe light emitted from the light source and the voltages applied to thepiezo-electric medium layer.

In an eighth aspect of the invention, the control means of theinformation recording/reproducing apparatus according to the seventhaspect above, at least when recording information to the informationrecording medium with the light beam for recording information, controlsthe diffraction efficiency so that the light beam power of thediffracted light assumes a level that does not erase information on theinformation recording medium by setting the voltage applied to thepiezo-electric medium layer to a predetermined voltage level.

According to the information recording/reproducing apparatus in theseventh or eighth aspect, it is possible to variably control thediffraction efficiency of a variable optical element by adjusting thevoltages applied to a piezo-electric medium layer. Based on this, it ispossible to eliminate problems where information on an informationrecording medium is unnecessarily erased by appropriately adjusting thepower of the light beam for recording information to or reproducinginformation from an information recording medium.

In a ninth aspect of the invention, the informationrecording/reproducing apparatus according to the eighth aspect furthercontains a crosstalk canceller circuit that suppresses crosstalkcomponents based on the information output by the photodetector while itdetects the reflected light.

An information recording/reproducing apparatus having such aconstruction provides for the reproduction of information withsuppressed crosstalk components based on the detected results detectedby the photodetector while reproducing information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a construction of a pickup apparatus accordingto the present embodiment of the invention;

FIG. 2A through FIG. 2D are views showing a structure of a variableoptical element according to the present embodiment of the invention;

FIG. 3A through FIG. 3G are view showing a production method for avariable optical element according to the present embodiment of theinvention;

FIG. 4 is a view for explaining operation of a pickup apparatus and aninformation recording/reproducing apparatus according to the presentembodiment of the invention;

FIG. 5 is a block diagram showing a construction of an informationrecording/reproducing apparatus according to the present embodiment ofthe invention;

FIG. 6 is a block diagram showing a construction of a crosstalkcanceller circuit provided in an information recording/reproducingapparatus;

FIG. 7 is a sectional view showing another structure of a variableoptical element;

FIG. 8 is a sectional view showing yet another structure of a variableoptical element;

FIG. 9 is a sectional view showing yet another structure of a variableoptical element;

FIG. 10 is a sectional view showing yet another structure of a variableoptical element;

FIG. 11 is a sectional view showing yet another structure of a variableoptical element;

FIG. 12A and FIG. 12B are sectional views showing still other structuresof a variable optical element; and

FIG. 13 is a sectional view schematically showing a structure of aninformation recording medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of a variable optical element, apickup apparatus, and an information recording/reproducing apparatusaccording to the present invention will be described with reference tothe drawings.

FIG. 1 is a constructional view showing a construction of a pickupapparatus, FIG. 2 are views showing a structure of a variable opticalelement, FIG. 3 are views showing a production method of a variableoptical element, FIG. 4 is a view for explaining operation of a variableoptical element and a pickup apparatus, FIG. 5 is a block diagramshowing a construction of an information recording/reproducingapparatus, and FIG. 6 is a block diagram showing a structure of acrosstalk canceller circuit provided in an informationrecording/reproducing apparatus.

In FIG. 1, the pickup apparatus 100 comprises: a light source 1 whichemits a laser beam Ha, a first beam splitter 2, quarter wavelengthplates 3 and 4 which are positioned so that each of them faces one oftwo sides of the first beam splitter 2, a variable optical element 5positioned to face the outside of the quarter wavelength plate 3, areflector 6 positioned to face the outside of the quarter wavelengthplate 4, a second beam splitter 7, a collimating lens 8, a quarterwavelength plate 9, an objective lens 10 positioned to face aninformation recording medium 13, a condenser lens 11, and aphotodetector 12, wherein these constituent elements 1 to 12 aredisposed along an optical axis OA.

The light source 1, containing a semiconductor laser (not illustrated)pointed along the optical axis OA, emits the linear-polarized laserbeam-Ha from the semiconductor laser to the first beam splitter 2.

The laser beam Ha, which is emitted from the light source 1, isreflected by the first beam splitter 2, then transmitted through thequarter wavelength plate 3 to be made incident onto the variable opticalelement 5, and further reflected by the variable optical element 5. Thereflected laser beam Hb is transmitted through the quarter wavelengthplate 3 again, then transmitted through the first beam splitter 2,further transmitted through the quarter wavelength plate 4 to be madeincident onto the reflector 6, and reflected by the reflector 6. Thelaser beam Hc reflected by the reflector 6 is transmitted through thequarter wavelength plate 4 again, and reflected by the first beamsplitter 2 to be emitted to the second beam splitter 7.

In other words, the laser beam Ha emitted from the light source 1 isreflected by the first beam splitter 2 to the quarter wavelength plate3. Since the laser beam Hb which is made incident onto the first beamsplitter 2 from the quarter wavelength plate 3 is transmitted throughthe quarter wavelength plate 3 twice and returned, it is transmittedthrough the first beam splitter 2 to enter the quarter wavelength plate4. Further, since the laser beam Hc which enters the first beam splitter2 from the quarter wavelength 4 is transmitted through the quarterwavelength plate 4 twice and returned, it is reflected by the first beamsplitter 2 to the second beam splitter 7.

The laser beam Hc which is emitted to the second beam splitter 7 fromthe first beam splitter 2 as described above is transmitted through thesecond beam splitter 7 to be collimated by the collimating lens 8, thenpasses through the quarter wavelength plate 9, and is irradiated ontothe information recording medium 13 as light beams MB(0), SB(−1), andSB(+1), which are described below, after being converged by theobjective lens 10.

In addition, the reflected beams RMB(0), RSB(−1), and RSB(+1), which arerespectively generated from the light beams MB(0), SB(−1), and SB(+1)reflected by the information recording medium 13, pass through theobjective lens 10, the quarter wavelength plate 9, and the collimatinglens 8, and they are further reflected by the second beam splitter 7 andemitted to the condensing lens 11. The condensing lens 11 condenses thebeams RMB(0), RSB(−1), and RSB(+1) reflected by the second beam splitter7, and emits them to the photodetector 12. The photodetector 12 receivesthe reflected beams RMB(0), RSB(−1), and RSB(+1), and thenphoto-electrically converts the beams into electric signals S_(MB(0)),S_(SB(−1)), and S_(SB(+1)) respectively to output them.

The variable optical element 5 has a structure as shown in FIG. 2A toFIG. 2D. As shown in the perspective view of the FIG. 2A, its structureis such that a grating portion 5 b of a reflective type is formed as onebody on a semiconductor substrate 5 a which is the reference medium, andan appropriate voltage V is applied by the voltage control circuit 14,between the electrode 5 c formed on the grating portion 5 b and theelectrode 5 b formed on the back side of the semiconductor substrate 5a.

Further, as shown in the planar drawing of FIG. 2B, the grating portion5 b is so shaped that a plurality of slit-like rectangular grooves 16and a plurality of convex portions 17 (hereinafter, referred to asconvexities) adjacent to each of the rectangular grooves 16 are formedone by one at a certain pitch distance D in a cyclic manner, thereby thefirst area having the plurality of convexities 17 and the second areahaving the plurality of rectangular grooves 16 are formed.

Still further, as shown in the longitudinal section of FIG. 2C (alongitudinal section along X—X indicated in FIG. 2B), each convexity 17has a layered structure which is formed on the semiconductor substrate 5a and comprised of a piezo-electric element layer 17 a, formed bypiezo-electric semiconductor having a piezo-electric effect or otherpiezo-electric media, an electrode layer 17 b, and a dielectricreflector layer 17 c for reflecting light beams. At the bottom part ofeach rectangular groove 16, a dielectric reflector layer 16 a forreflecting light beams is formed on the semiconductor substrate 5 a. Inaddition, aforementioned electrode 5 c is disposed and formed on the topsurface of the electrode layer 17 b, and an electrode layer 5 d isformed on the bottom side of the semiconductor substrate 5 a byevaporation.

When a voltage V is applied between the electrode 5 c and the electrodelayer 5 d, piezo-electric semiconductor layer 17 a experiences changesin thickness because of the piezo-electric effect corresponding to theelectric field caused by the applied voltage V, whereby the height H ofthe dielectric reflector layer 17 c of the convexity 17 whichcorresponds to the dielectric reflector layer 16 a of the rectangulargroove 16 as shown in the longitudinal section of FIG. 2D (thelongitudinal section of a representative part of FIG. 2C) is changed.

Next, a production method of the variable optical element 5 will bedescribed referring to the sectional views in FIG. 3A through FIG. 3G.

The variable optical element 5 is produced in a semiconductor productionprocess. First, a silicon semiconductor substrate 5 a of either a P or Ntype is prepared (FIG. 3A) and a piezo-electric element layer 17 acomprising media with piezo-electric effect such as ZnO, ZnS, CdS, CdTe,InSb, BaTiO3 (barium titanate), and KNaC₄H₄O₆ (Rochelle salt) (FIG. 3B)is formed on the semiconductor substrate 5 a by sputtering. Next, ametal electrode layer 17 b is deposited on the piezoelectric elementlayer 17 a by sputtering (FIG. 3C). In the present embodiment, thethickness of the piezo-electric element layer 17 a is set toapproximately 120 μm.

Next, a photoresist pattern PL is patterned on the electrode layer 17 bby photolithography (FIG. 3D). At this time, the photoresist pattern PLis patterned so that width of both the rectangular groove 16 and theconvexity 17 is ½ of the pitch distance D. In the present embodiment,the pitch distance D is set to approximately 25 μm.

Next, using the photoresist pattern PL as a mask, the electrode layer 17b and the piezo-electric element layer 17 a are removed as far as thesemiconductor substrate 5 a by dry etching (RIE) but leaving the part ofthe electrode layer 17 b and the piezo-electric element layer 17 a thatis masked by the photoresist pattern (FIG. 3E).

Next, after the photoresist pattern PL is removed by using a remover(FIG. 3F), and an electrode 5 c is formed on the electrode layer 17 b.

Next, a layer of dielectric reflector is formed on top of the exposedelectrode layer 17 b and semiconductor substrate 5 a by evaporation toform the dielectric reflector layer 16 a of the rectangular groove 16and the dielectric reflector layer 17 c of the convexity 17 respectivelyas shown in FIG. 2C (FIG. 3G). Thus a grating portion 5 b is completed.

Finally, a metal electrode layer 5 d is formed on the back of thesemiconductor substrate 5 a by evaporation to complete a variableoptical element 5.

The variable optical element 5 produced as described above, according toFIG. 1, is arranged with its grating portion 5 b facing the quarterwavelength plate 3 and arranged so that the direction in which therectangular grooves 16 and the convexities 17 are arrayed isperpendicular to the polarization direction of the laser beam Ha whichis made incident through the quarter wavelength plate 3.

Again according to FIG. 1, when the light beam Ha emitted by the lightsource 1 is made incident onto the variable optical element 5 throughthe beam splitter 2 and the quarter wavelength plate 3, the variableoptical element 5 does not simply reflect the light beam Ha coming fromthe quarter wavelength plate 3 but diffracts it based on the first orderdiffraction efficiency η which is determined by the rectangular grooves16 and the convexities 17 of the grating portion 5 b, and emits, to thequarter wavelength plate 3, a 0th order diffracted light, a −1st orderdiffracted light, and a +1st order diffracted light which are generatedby the diffraction. In other words, a laser beam H1 becomes a 0th orderdiffracted light, a −1st order diffracted light, and a +1st orderdiffracted light.

Thus, the light beams MB(0), SB(−1), and SB(+1) that are converged bythe objective lens 10 to be irradiated to the information recordingmedium 13 are generated based on the 0th order diffracted light, the−1st order diffracted light, and the +1st order diffracted light. Asshown in the plan view of FIG. 4, three beams, namely, the light beamMB(0) (hereinafter referred to as the main beam) generated by the 0thorder diffracted light, the light beam MB(−1) (hereinafter referred toas the sub-beam) generated by the −1st order diffracted light, and thelight beam MB(+1) (hereinafter referred to as the sub-beam) generated bythe +1st order diffracted light, are irradiated onto the informationrecording medium 13. In addition, the reflected light beams RMB(0),RSB(−1), and RSB(+1), which are generated by reflecting the light beamsMB(0), SB(−1), and SB(+1) by the information recording medium 13, aredetected by the photodetector 12 shown in FIG. 1.

FIG. 4 shows a case where light beams MB(0), SB(−1), and SB(+1) areirradiated onto a phase-change type disc-shaped information recordingmedium 13 which has a layered structure consisting of a light-incidentlayer 13 a, a recording layer 13 b, and a substrate 13 c. The samefigure indicates the positions of irradiated beams of MB(0), SB(−1), andSB(+1) with respect to the grooves G and the lands L while recording andreproducing information. In addition, for the convenience ofexplanation, the groove G1 is shown as corresponding to the main trackto and from which information is recorded or reproduced, and the groovesG2 and G3 are shown as corresponding to the adjacent tracks. Inaddition, with respect to the relative movements the pickup apparatus100 makes while recording and reproducing information, the direction oflinear scanning is indicated as θs and the direction perpendicular tothe direction of linear scanning θs (hereinafter, referred to as theradial direction) is indicated as θr.

Now, power values P(0), P(−1), and P(+1) of corresponding light beamsMB(0), SB(−1), and SB(+1) are determined according to the first orderdiffraction efficiency η of the grating portion 5 b formed on thevariable optical element 5. Where the total power Pad of the light beamsMB(0), SB(−1), and SB(+1), the power Pa of the laser beam Ha emittedfrom the light source 1, and the attenuation rate α of the laser beam Haby the time it reaches the information recording medium 13, thefollowing equations (1), (2), and (3) are provided:P(0)≈(1−2×η)×Pad≈(1−2×η)×α×Pa  (1)P(−1)≈η×Pad≈η×α×Pa  (2)P(+1)≈η×Pad≈η×α×Pa  (3)

In addition, the first order diffraction efficiency η is a coefficientwhose value is determined based on the pitch distance D of therectangular grooves 16 and the convexities 17 formed on the grading 5 bas shown in FIG. 2B and based on the height H between the dielectricreflector layers 17 c and 16 a as indicated in FIG. 2D. Further, sincethe thickness of the piezo-electric element layer 17 a changes accordingto the applied voltage V thereby changing the height H, it becomespossible to change the first order diffraction efficiency η bycontrolling the applied voltage of V, and thus adjustment of the powervalues P(0), P(−1), and P(+1) also becomes possible accordingly.

Incidentally, as a result of setting the thickness of the piezo-electricelement layer 17 a to approximately 120 μm and the width of theconvexities 17 to a half of the pitch distance D (approximately 25 μm),if the applied voltage V is changed from 0 volts to approximately 60volts, the height H increase by approximately 15 nm. Based on this, if ablue semiconductor laser is used in the light source, the first orderdiffraction efficiency η for the laser beam Ha can be changed byapproximately 25%.

In the present embodiment of the invention, the power of the so-calledmain beam is set to 0.5 mW and the sub-beam to 0.1 mW when informationis reproduced. In order to achieve such a condition, the diffractionefficiency η is set to approximately 20%. Further, when recordinginformation, the main beam is set to 6 mW and the sub-beams set toaround 0.6 mW. To achieve such a condition the diffraction efficiency isset to approximately 10% or less.

Next, referring to FIG. 5 and FIG. 6, a description will be given of astructure of an information recording/reproducing apparatus 200 whichuses a pickup apparatus 100 having a variable optical element 5. FIG. 5is a block diagram showing a construction of an informationrecording/reproducing apparatus 200, and FIG. 6 is a block diagramshowing a structure of a crosstalk canceller circuit 300 provided in aninformation recording/reproducing apparatus 200.

In FIG. 5, the information recording/reproducing apparatus 200comprises: a driving motor 18 which rotate an information recordingmedium 13 while-supporting it at the same time, a pickup apparatus 100as shown in FIG. 1, a voltage control circuit 14 which applies voltage Vto the variable optical element 5 provided in the pickup apparatus 100,a crosstalk canceller circuit 300, a recording/reproduction processcircuit 19, a servo circuit 20, and a system controller 21.

The recording/reproduction process circuit 19, while recordinginformation, performs such processes as encoding on supplied contentsignal Sin, supplies it to the light source 1 provided in the pickupapparatus 100 and causes the light source 1 to set the power Pa of thelaser beam Ha to the power for recording Paw so as to emit.Additionally, while reproducing information, the recording/reproductionprocess circuit causes the light source 1 to set the power Pa of thelaser beam Ha to the power for reproducing Par so as to emit, performssuch process as decoding on read signal So which is read out from aninformation recording medium 13 and supplied via the crosstalk cancellercircuit 300, and generates reproduced signal Sout and outputs it.

The servo circuit 20 controls the rotational speed of the driving motor18 and causes the pickup apparatus 100 to move at a predetermined linearspeed relative to the information recording medium 13 by controlling thecarriage mechanism (not illustrated) which moves the pickup apparatus100 back and forth along the radial direction θr of the informationrecording medium 13.

In the system controller 21 a microprocessor (MPU) for controlling theentire information recording/reproducing apparatus 200 is provided.

In an information recording/reproducing apparatus 200 having such astructure, if a user inserts a phase-change type information recordingmedium 13 and issues a command to the system controller 21 to startrecording information, the recording of information is started.

While recording information as above, the voltage control circuit 14applies a predetermined voltage Vw to the variable optical element 5,which sets the grating portion 5 b to the first order diffractionefficiency ηw for recording information. Further, while the first orderdiffraction efficiency ηw is set in this state, therecording/reproduction process circuit 19 supplies signals to berecorded onto the light source 1 and causes it to emit the laser beam Hahaving the power for recording.

Based on the above, as shown in FIG. 4, the main beam MB(0) isirradiated on the main track G1 and the sub-beams SB(−1) and SB(+1) areirradiated on the adjacent tracks G2 and G3 respectively, and therebythe recording of information by the main beam MB(0) on the track G1 isperformed.

In this case, the power Paw of the laser beam Ha and the first orderdiffraction efficiency ηw of the grating portion 5 b are determinedaccording to the types of the information recording medium 13.

In other words, where the power which can record information(hereinafter, referred to as recording power) by causing phase changesin the recording layer 13 b of the information recording medium 13 isgiven as Pwt, the power which can erase information already recorded(hereinafter, referred to as erasing power) by causing phase changes inthe recording layer 13 b of the information recording medium 13 is givenas Per, the power of the main beam MB(0) is given as P(0), the power ofthe sub-beam SB(−1) is given as P(−1), and the power of the sub-beamSB(+1) is given as P(+1), the power Paw of the laser beam Ha is set sothat the equations (4) to (8) are satisfied and the first orderdiffraction efficiency ηw is set by the voltage Vw:Pwt≦P(0)  (4)P(−1)<Pes  (5)P(+1)<Pes  (6)ηw<Pes/Pwt  (7)Paw={P(0)+P(−1)+P(+1)}/α  (8)

As shown in the above, if the power Paw of the laser beam Ha and thefirst order diffraction efficiency ηw of the grating portion 5 b areset, information can be recorded in the main track G1 with the main beamMB(0) having appropriate power P(0) while preventing the sub-beamsSB(−1) and SB(+1) from erasing or destroying information in the adjacenttracks G2 and G3.

Next, if a user mounts a phase-change type information recording medium13 and issues a command to the system controller 21 to start reproducinginformation, the reproduction of information is started.

While the information is produced, the voltage control circuit 14applies a predetermined voltage Vr to the variable optical element 5,whereby it sets the grating portion 5 b to the first order diffractionefficiency ηr for reproducing information. While the first orderdiffraction efficiency θr is set in this condition the light source 1 iscaused to emit the laser beam Ha having the power Pr for reproduction.

Based on the above, as shown in FIG. 4, the main beam MB(0) isirradiated on the main track G1 and the sub-beams SB(−1) and SB(+1) areirradiated on the adjacent tracks G2 and G3 respectively, and therebyread-out of information by the main beam MB(0) from the track G1 isperformed.

In this case, the power Par of the laser beam Ha and the first orderdiffraction efficiency ηr of the grating portion 5 b are determinedaccording to the type of the information recording medium 13. In otherwords, based on the total power Pad (=P(0) +P(−1)+P(+1)) of the beamsMB(0), SB(−1), and SB(+1), the erasing power Per, and the power Prdnecessary to read out information from the main track G1, the power Parof the laser beam Ha is set so that the equations (8) to (12) below aresatisfied and the first order diffraction efficiency ηr is set by thevoltage Vr:P(0)≈Prd  (8)P(−1)<Per  (9)P(+1)<Per  (10)ηr>(1−Per/Pad)/2  (11)Par={P(0)+P(−1)+P(+1)}/α  (12)

When the power Par of the laser beam Ha and the first order diffractionefficiency ηr of the grating portion 5 b are set as shown in the above,information can be reproduced from the main track G1 by the main beamMB(0) while preventing the main beam MB(0) and the sub-beams SB(−1) andSB(+1) from erasing or destroying the information in each track of G1,G2 and G3.

Further, the photodetector 12 receives light reflected beam RB(0)generated by the main beam MB(0) and reflected beams RMB(0), RSB(−1),and RSB(+1) which are generated by the sub-beams SB(−1) and SB(+1), andsupplies the electric signals S_(MB(0)), S_(SB(−1)), and S_(SB(+1)) tothe crosstalk canceller circuit 300 shown in FIG. 6.

The crosstalk canceller circuit 300 comprises: waveform formationcircuits 22, 23, and 24, which shape waveforms of electric signalsS_(MB(0)), S_(SB(−1)), and S_(SB(+1)) output from the photodetector 12into binary logic signals S_(MB(0)), S_(SB(−1)), and S_(SB(+1)); CCDmemories 25, 26, and 27 serving as FIFO (first in first out) memories totemporarily store each corresponding signal of S_(MB(0)), S_(SB(−1)),and S_(SB(+1)) after the waveforms thereof have been formed; asynchronization detection circuit 28; a timing adjustment circuit 29;and a noise canceller circuit 30.

Here, the synchronization detection circuit 28 detects the physicaladdress information of the grooves G1, G2, and G3 which are contained inthe logic signals S_(MB(0)), S_(SB(−1)), and S_(SB(+1)), and thereby,based on the detected result, judges the delay time τd of the light beamSB(−1) with respect the light beam MB(0) and the lead time τf of thelight beam SB(+1) with respect to the light beam MB(0), in the linearscanning direction θr as shown in FIG. 4. The same circuit generates asynchronization signal CK indicating the delay time τd and lead time τfwith reference to the light beam MB(0) and supplies it to the timingadjustment circuit 29.

The timing adjustment circuit 29, based on the timing of thesynchronization signal CK, reads out the logic signal S_(MB(0)) recordedin the CCD memory 25, and forwards the logic signal S_(MB(0)) as thelogic signal S(0) to the noise canceller circuit 30. Further, the samecircuit reads out the logic signal SSB(−1) from the CCD memory 26 at atiming earlier than the readout timing of the logic signal S_(MB(0)) bythe delay time τd, and forwards the logic signal S_(SB(−1)) as the logicsignal S(−1) to which timing adjustment has been performed to the noisecanceller circuit 30. Further, the same circuit reads out the logicsignal S_(SB(+1)) from the CCD memory 27 at a timing later than thereadout timing of the logic signal S_(MB(0)) by the lead time τf, andforward the logic signal S_(SB(+1)) as the logic signal S(+1) to whichtiming adjustment has been performed to the noise canceller circuit 30.

As described above, by forwarding, to the noise canceller circuit 30,the logic signals S_(MB(0)), S_(SB(−1)), and S_(SB(+1)), recorded in theCCD memories 25, 26, and 27 respectively after timing adjustment hasbeen performed based on the delay time τd and the lead time τf, thelogic signals S_(MB(0)), S_(SB(−1)), and S_(SB(+1)) including with themthe positional information of the grooves G1, G2, and G3 relative to theradial direction θr as shown in FIG. 4 are supplied to the noisecanceller circuit 30.

That is, though the light beams MB(0), SB(−1), and SB(+1) are actuallyshifted in terms of phase in the direction of linear scanning θs, thetiming adjustment circuit 29 performs the above described timingadjustment based on the synchronization signal CK, and whereby the logicsignals S_(MB(0)), S_(SB(−1)), and S_(SB(+1)) which are obtained, whenthe light beams MB(0), SB(−1), and SB(+1) are irradiated, seemingly, inthe same phase in the direction of linear scanning θs (in other words,their beam spots are aligned in the radial direction θr) are supplied tothe noise canceller circuit 39.

The noise canceller circuit 30 generates the readout signal So with thecrosstalk component suppressed by canceling out the crosstalk componentcontained in the logic signal S(0) by logic signals S(−1) and S(+1), andsupplies it to the recording/reproduction process circuit 19, therebygenerating the reproduced signal Sout which should be originallyreproduced.

In addition, when information is reproduced from a non-phase-changetype, reproduction-only information recording medium, it is possible toreproduce information in a similar way as described above so as toreproduce information from the phase-change type information recordingmedium 13 and generate a reproduced signal Sout whose crosstalkcomponent is suppressed.

As described above, the pickup apparatus and an informationrecording/reproducing apparatus of the present embodiment contains avariable optical element 5 whose first order diffraction efficiency ηchanges according to the applied voltages V and the first orderdiffraction efficiency η is adjusted depending on when information isrecorded and when information is reproduced. Thereby, for recording ofinformation while adjacent tracks G2 and G3 of the information recordingmedium 13 are irradiated with sub-beams SB(−1) and SB(+1) having suchlow power P(−1) and P(+1) as not to erase or destroy information, by amain beam MB(0) having appropriate power, information is recorded on themain track G1.

In other words, the variable optical element 5 has a characteristic inwhich its first order diffraction efficiency η is changed according tothe applied voltages V. When the applied voltage V is lowered, the firstorder diffraction efficiency η is decreased, and when the voltage V israised, the first order diffraction efficiency η is increased. In turn,when the first order diffraction efficiency η is lowered, power of the−1st order diffracted light and +1st order diffracted light is reducedand, relatively, the power of the 0th order diffracted light isincreased. On the other hand, when the first order diffractionefficiency η is raised,, power of the −1st order diffracted light andthe +1st order diffracted light is increased and, relatively, power ofthe 0th order diffracted light is reduced.

Therefore, when information is recorded, a low voltage Vw for recordingis used to control the first order diffraction efficiency η, whereby thepower of the −1st order diffracted light and +1st order diffracted lightis lowered and accordingly, it becomes possible to increase the power ofthe 0th order diffracted light, and thus the power of the main beamMB(0) can be set to a level suitable for recording information and thesub-beams SB(−1) and SB(+1) can be set to a low level which does notcause erasure or destruction of the information.

On the other hand, when information is reproduced, by irradiating themain beam MB(0) and sub-beams SB(−1) and SB(+1) respectively having suchlow power levels P(0), P(−1), and P(+1) as not to erase or destroyinformation are, respectively, irradiated onto the main track G1 andsub-tracks G2 and G3 of the information recording medium 13, the mainbeam MB(0) having appropriate power P(0) can be used to reproduceinformation from the main track G1. In particular, since this methoddoes not erase or destroy any information recorded in the adjacenttracks G2 and G3, a crosstalk cancellation technique can be effectivelyused.

In other words, as described above, the variable optical element 5 has acharacteristic where it changes the first order diffraction efficiency ηcorresponding to the applied voltage V, thereby changing the power ofthe −1st order diffracted light and the +1st order diffracted lightrelatively to the power of the 0th order diffracted light,and-therefore, when information is reproduced, by controlling so thatthe first order diffraction efficiency η is increased by a high voltageVr for reproduction, it becomes possible to raise the power of the −1storder diffracted light and the +1st order diffracted light and to lowerthe power of the 0th order diffracted light accordingly. Thus,appropriately controlling the first order diffraction efficiency η makesit possible to set the power of the main beam MB(0) and the sub-beamsSB(−1) and SB(+1) to an appropriate power which does not erase ordestroy information and to reproduce the information.

In addition, by adjusting the first order diffraction efficiency η ofthe variable optical element 5, depending on the cases where informationis recorded to and reproduced from, a phase-change type informationrecording medium and where information is reproduced from anon-phase-change, reproduction-only type information recording medium,it is easy to generate the main beam MB(0) and sub-beams SB(−1) andSB(+1) having an appropriate power for each type of informationrecording media. Therefore, this adjusting makes it possible to providea pickup apparatus and an information recording/reproducing apparatuswith high compatibility.

In addition, since the piezo-electric element layer 17 b of the variableoptical element 5 has a characteristic such that it rapidly changes itsthickness according to the applied voltage V (characteristic ofdistortion), it provides for recording of information and reproducing ofinformation can be performed with high responsiveness even whenrecording and reproducing are switched one after the other.

In addition, in the present embodiment, descriptions thus far areprovided in the case where a variable optical element 5 is used as areflective grating for generating a main beam MB(0) and sub-beams SB(−1)and SB(+1) having appropriate power levels, however, this variableoptical element 5 may be used as an optical modulation element for otherpurposes. Further, in the present embodiment, as shown in FIG. 1, thevariable optical element 5 is arranged to be perpendicular to theincident-light beam Ha, however, it may be arranged diagonally dependingon the optical system and used.

In the preferred embodiments of the invention thus far, descriptions areprovided in the case where only one layer of piezo-electric element 17 ais formed in convexities 17 of the variable optical element 5. However,as shown in the longitudinal section of FIG. 7, a piezo-electric layer17 a′ and an electrode layer 17 b′ can further be formed between theelectrode layer 17 b and the dielectric reflector layer 17 c, therebyapplying a first applied voltage V1 between the electrode layers 17 b′and 17 b and a second applied voltage V2 between the electrode layers 17b and 15 d. In such a structure, because the thickness, of thepiezo-electric element layers 17 a and 17 a′ can be changed to a greaterdegree according to the applied voltages V1 and V2, the first orderdiffraction efficiency η can be controlled in a wider range, thusproviding for recording and reproducing information to and from agreater variety of information recording media. For example, it becomespossible to perform recording and reproducing information to and from aninformation recording media with one recording layer and a multi-layeredinformation recording media with multiple recording layers using thesame pickup apparatus. Further, it becomes possible to rapidly switchbetween recording to and reproducing from one of the multiple recordinglayers and recording to and reproducing from the rest of the multiplerecording layers of the same information recording media.

In addition, the piezo-electric element layer 17 a′ and electrode layer17 b′ shown in FIG. 7 can be further added in a greater number of pairsto allow control of the first order diffraction efficiency η over a muchgreater range.

Further, in the variable optical element 5 shown in FIG. 2A through FIG.2D and FIG. 7, dielectric reflector layers 16 a and 17 c are provided toreflect light, however, as shown in FIG. 8, it is possible to coat atransparent media PE over the electrode layer 17 b of the convexities 17and the upper surface of the semiconductor substrate 5 a serving asrectangular grooves 16 by spin coating so as to fill the rectangulargrooves 16 with this media PE. Having such a structure allows switchingbetween two states where the first order diffraction does not occur andwhere the first order diffraction occurs depending on the appliedvoltage V, thus achieving a variable optical element having the samefunction as the variable optical element 5 as shown in FIG. 2A throughFIG. 2D and FIG. 7.

Further, the variable optical element 5 shown in FIG. 2A through FIG. 2Dis presented as having the grating portion 5 b consisting of narrowrectangular-shaped grooves 16 and convexities 17 which are implementedone by one in a cyclic manner. However, without being limited to such astructure, the grating portion 5 b can have a structure as shown in theperspective view of FIG. 9 where bent line-shaped grooves 31, whichfollow the wave front to be given to diffracted light, and convexities32 are implemented one by one in a cyclic manner.

In addition, the variable optical element 5 shown in FIG. 2A throughFIG. 2D is presented as having the grating portion 5 b withrectangular-shaped grooves 16 which are surrounded by the portion of thesame convexities as the convexities 17. However, without being limitedto such a structure, a portion of the convexities may be so formed thatthey collectively take a shape like a comb which defines rectangulargrooves 16 and convexities 17 as shown in the perspective view of FIG.10.

In addition, as shown in the perspective view of FIG. 11, each of theconvexities 17 may be separated and have an electrode formed in them, towhich applied voltage V may be applied. However, in FIG. 11, instead ofapplying a common applied voltage V to all of the convexities 17,voltages may be applied independently to individual convexities 17.Because, if voltages are applied independently, the thickness of eachconvexity 17 can be controlled independently, and variable opticalelements with diverse optical characteristics can be achieved.

Further, as shown in FIG. 3A through FIG. 3G, the variable opticalelement 5 has a structure where a piezo-electric element layer 17 a anda reflector layer 17 c are formed in the convexities 17 and only areflector layer 16 a is formed in the rectangular grooves 16. However,the present invention is not limited to such a structure.

As a modified example, as shown in FIG. 12A, the piezo-electric elementlayer 17 a″ which has less thickness than a piezo-electric element layer17 a may be formed. By forming a reflector layer 16 a on top of 17 a″,rectangular grooves 16 may be formed which are lower in height thanconvexities 17.

Even though such a structure can be achieved by such techniques asphotolithography, etching, sputtering, and gas phase growth method, forexample, by reducing the amount of etching in the areas of thepiezo-electric element layer 17 a which correspond to the rectangulargrooves 16 during the etching process as shown in FIG. 3E, portionshaving a thin layer of piezo-electric element remains which can be usedas the piezo-electric element layer 17 a″ of a lesser thickness.

Wiring can be formed to individually connect the thin piezo-electricelement layer 17 a″ and the thick piezo-electric element layer 17 a toapply different voltages to each wiring for controlling the amount ofdistortion caused in each layer. Or common wiring can be formed toconnect both the thin piezo-electric element layer 17 a″ and the thickpiezo-electric element layer 17 a, which allows control of the variedamounts of distortion between the layers of different thickness eventhough the voltage applied may be the same.

Further, as a modified example of a variable optical element 5 shown inFIG. 8, in a similar manner as employed for the structure in FIG. 12A apiezo-electric element layer 17 a″ having a lesser thickness than apiezo-electric element layer 17 a is formed in the rectangular grooves16 and then the whole side may be covered with a transparent media PE asshown in FIG. 12B. Such a structure of FIG. 12B can be achieved in asimilar way as the case of FIG. 12A by appropriately controlling theamount of etching.

Additionally, in a structure shown in FIG. 12B, wiring can be formedindividually to each of the piezo-electric element layers 17 a and 17 a″for independent voltage control. Also, common wiring can be formed toboth piezo-electric element layers 17 a and 17 a″ to apply the samevoltage. In other words, the amount of distortion can be controlledaccording to the difference in thickness between the piezo-electricelement layers 17 a and 17 a″ even though the control voltage is thesame for both. In addition, if a common control voltage is applied, itcan be structured so that transparent electrodes (ITO) are formed as atransparent medium PE and a common control voltage is applied to thetransparent electrodes.

As has been described, a variable optical element of the presentinvention is given a structure such that, when light is incident on thefirst and the second areas, it reflects the light imparting opticalchanges to its wave front based on changes in the opticalcharacteristics of the first and the second areas caused by thepiezo-electric effect of the piezo-electric medium layer. Therefore, bycontrolling the piezo-electric effect of the piezo-electric medium layerit becomes possible to impart various optical changes to the incidentlight. This can be used, for example, to appropriately control opticalcharacteristics of light beams irradiated onto an information recordingmedium for the purpose of recording or reproducing information.

In addition, a pickup apparatus of the present invention is providedwith a light source which emits light onto the first and the secondareas of a variable optical element, and an optical system whichgenerates light beams for recording information and light beams forreproducing information based on diffracted light caused when the lightis diffracted by the variable optical element and nondiffracted light.Therefore, for example, by controlling the voltage applied on thevariable optical element, it is possible to generate light beams havinga power appropriate for recording information on an informationrecording medium, that is, a power which will not erase or destroy anyinformation already recorded on the information recording medium, and itis also possible to generate light beams having power appropriate forreproducing information from an information recording medium, that is, apower which will not erase or destroy any information already recordedon the information recording medium.

In addition, an information recording/reproducing apparatus of thepresent invention is enabled, by containing a pickup apparatus which hasa variable optical element, to detect a light beam with a photodetectorwherein the light beam is first irradiated onto an information recordingmedium for recording information then reflected by the informationrecording medium, and then based on the result of detection it cangenerate control signals, such as a tracking error signal for example,for performing an appropriate information recording process. In such acase, it can generate light beams for recording information having apower which will not cause erasure or destruction of information alreadyrecorded on the information recording medium. Further, it is enabled todetect a light beam with a photodetector wherein the light beam is firstirradiated onto an information recording medium for reproducinginformation then reflected by the information recording medium and then,based on the result of detection, it can generate control signals forperforming an appropriate information reproduction process. In this casealso, it can generate light beams for reproducing information having apower which will not cause erasure or destruction of information alreadyrecorded on the information recording medium. Additionally, it canreproduce information with its crosstalk component suppressed based onthe result detected by the photodetector.

Further, according to the variable optical element, pickup apparatus,and information recording/reproducing apparatus, because a light beamappropriate for each type of information recording media can begenerated depending on when information is recorded to and reproducedfrom a phase-change type information recording medium or wheninformation is reproduced from a non-phase-change, reproduction-onlytype information recording medium, advantageous effects can be attainedsuch that a highly compatible pickup apparatus and informationrecording/reproducing apparatus can be provided.

1. A variable optical element comprising: a reference medium; a firstarea with a piezo-electric medium layer having a piezo-electric effect;and a second area without said piezo-electric medium layer, the firstand second areas being formed on the top surface of the referencemedium, wherein optical changes are imparted on the wave front of lightmade incident onto said first and said second areas to reflect the lightbased on changes in optical characteristics of said first and saidsecond areas caused by the piezo-electric effect of said piezo-electricmedium layer.
 2. A variable optical element according to claim 1,wherein a plurality of pairs of said first and said second areas areformed one after another in a cyclic manner.
 3. A variable opticalelement according to claim 2, wherein said piezo-electric medium layerchanges in the thickness as a result of said piezo-electric effectcorresponding to voltages externally applied, and wherein diffractionefficiency is changed for the light made incident on said first and saidsecond areas based on phase changes in said first and said second areasdue to said changes in thickness.
 4. A variable optical elementaccording to claim 1, wherein said piezo-electric medium layer changesin the thickness as a result of said piezo-electric effect correspondingto voltages externally applied, and wherein diffraction efficiency ischanged for the light made incident on said first and said second areasbased on phase changes in said first and said second areas due to saidchanges in thickness.
 5. A variable optical element according to claim1, further comprising, within the first area, at least one pair of anadditional piezo-electric medium layer and an electrode layer formed onthe piezo-electric medium layer so as to apply voltages to thepiezo-electric medium layer and the additional piezo-electric mediumlayer.
 6. A variable optical element according to claim 1, furthercomprising a transparent media with which the first and second areas arecovered over.
 7. A variable optical element according to claim 1,wherein a plurality of pairs of the first and second areas are formedone after another so as to have a structure so that bent line-shapedgrooves following a wave front to be given to diffracted light andconvexities are implemented one by one in a cyclic manner.
 8. A variableoptical element according to claim 1, further comprising dielectricreflector layers are provided on the first and second areasrespectively.